Triumph. That’s the look on President Harry Truman’s face. Sheer, unadulterated triumph. In fact, of the countless politics-related photographs made over, say, the past century, one would be hard-pressed to point to a more famous image than W. Eugene Smith’s shot of an ebullient Truman holding aloft a copy of the Chicago Tribune emblazoned with the now-legendary (erroneous) headline: DEWEY DEFEATS TRUMAN.

The reason for the picture’s immortality? It’s not the headline itself—although that titanic error is, in its own way, rather marvelous. Instead, the picture endures because of the look of unabashed, in-your-face delight in Truman’s eyes.

It is the greatest photograph ever made of a politician celebrating victory. Period.

The story behind the Tribune‘s notorious 1948 screw-up has, of course, been told again and again—here’s one easily digestible take, with the added bonus that it includes a reference to LIFE—but in truth, it’s not only the tale of the mistake itself that remains fascinating all these years later: it’s what Smith’s picture tells us about politics, photography and memory that raises the image from the merely great to the indispensable.

First, a brief discussion of the ’48 election itself. In what is generally regarded as the greatest upset in American political history, Truman beat the heavily-favored Republican governor of New York, Thomas Dewey, by a substantial Electoral College margin, 303 to 189, but by fewer than three million votes in the popular vote. (The right-wing, stridently segregationist “Dixiecrat” nominee, Strom Thurmond, won four states—Alabama, Mississippi, Louisiana and his home state of South Carolina—and 39 electoral votes in 1948.)

A full two days after the election, the president was on his way back to Washington from his home in Independence, Mo., when his train stopped in St. Louis. There, someone handed Truman a two-day-old copy of the Tribune. (One version has a staffer serendipitously finding the paper under a seat in the station.)

Maybe Truman had already heard about the Trib‘s embarrassing snafu, but had not yet held a copy in his hands. Perhaps this was the first time he had any inkling of how huge—and how hugely mistaken—the headline actually was. However it shook out, in Smith’s photograph of that priceless moment, Truman’s elation upon coming face to face with the dead-wrong assertion of his defeat is positively palpable.

Seeing the image today, it’s hard to believe that the photograph was not made on election night. After all, in an age of 24/7 news, when more and more media consumers get their breaking news via tweets and friends’ Facebook posts, and a quarter-hour constitutes a news cycle, the notion that anyone would bother referencing a newspaper (a newspaper, of all things!) 48 hours after an event seems a bit absurd.

It’s not that newsworthy events happened any slower back in the day. Crime, sex scandals, intrigue, sports upsets, financial tremors, political corruption, gossip—all of the messy, chaotic, riveting information that dominates today’s news was just as messy, chaotic and riveting 75 years ago. But the mechanisms for disseminating that information have gone through so many evolutions, and there are now so many means of hearing and seeing breaking news as it happens, that a news event from two days ago feels, frankly, like something out of the past.

Pundits might still be chattering about a resonant quote from a debate held two nights ago—but most everybody else has already engaged in the meme and moved on.

The photograph of a giddy Harry Truman showing the world a copy of the Chicago Tribune, on the other hand, is evidence not only of another time, but of another way of remembering. The picture feels like it could have been made—that it must have been made—on election night because, for the man in the photograph, both his victory and the paper’s humiliating mistake have been enshrined in a headline. The inescapable emotion in his face reflects not only the triumph of his political ideas in a hard-fought national contest, but his ability to revisit his election-night triumph by the simple act of gazing at a two-day-old paper.

The headline, DEWEY DEFEATS TRUMAN, was dead wrong. It would have to be changed, corrected, remade. In fact, by the time Smith took his famous picture in St. Louis, the headline would have been changed on subsequent editions of the paper. The Tribune‘s wildly inaccurate first draft of history would have been rewritten. The error would enter into journalistic legend—a cautionary tale taught in J-schools forever more.

But the thrill evident in the face of the man holding that paper remains as indelible today as when it was captured all those years ago, 48 hours after election night.

In that light, perhaps Smith’s photo is not the greatest picture ever made of a politician celebrating victory, after all. Instead, it’s the greatest picture ever made of a politician in the throes of remembering what sweet, improbable victory feels like, while holding aloft a document that, loudly and wrongly, shouts his defeat to the world.